The present invention relates to oil control rings and more particularly two-piece oil control rings which include a spacer-expander having an integral bottom segmented rail and a split or parted top rail ring.
Oil control rings are used in internal combustion engines to limit the flow of lubricant along the cylinder wall and into the combustion chamber. Excess amounts of lubricant are distributed onto the cylinder wall of the internal combustion engine during operation to lubricate the pistons and cylinder wall, clean the cylinder wall, cool the cylinder wall and pistons and to increase the effectiveness of the seal between the piston rings and the cylinder wall. Oil control rings are necessary for oil economy purposes, to control exhaust emissions and for proper engine operation.
Heretofore a wide variety of piston ring configurations have been proposed for such oil control purposes. These various proposals have included one-piece, two-piece, and three-piece configurations. Each of these configurations typically includes an upper rail structure and an axially spaced lower rail structure which engages the cylinder wall. One-piece oil control rings include a non-parted top rail and either non-parted, or segmented lower rail defining segments. Three-piece oil control rings include split or parted top and bottom rails and a spacer-expander which axially spaces the rails and biases them radially outwardly into engagement with the cylinder wall. Typically, the spacer-expander exerts the same radial force to tension on the top and bottom rails. It has been found, however, that the upper rail performs the majority of the oil control function. The split or parted rails are fairly rigid or non-flexible due to their annular configuration. The radial stiffness limits the ability of the split rail to conform to variations in the cylinder wall's surface.
In an attempt to increase the effectiveness of an oil control ring, reduce the weight and hence the inertia and to increase the flexibility and hence the ability of the ring to conform the cylinder wall variations, two-piece oil control rings have been proposed. The two-piece oil control rings typically employ a top, parted or split rail and a spacer-expander having integral therewith a plurality of circumferentially spaced segments. The segments define a segmented bottom rail which is more flexible than the split rail ring and hence more easily conforms to cylinder wall variations. Further, the segments reduce the overall weight of the oil control ring thereby reducing the inertia of the ring. Typically, however, the segmented spacer-expander due to its flexibility requires a latch to join the abutting ends for assembly purposes. Further, prior two-piece oil control rings have not been readily adaptable to varying ring groove depths. Typically, the overall radial depth of the ring and the radial depth of the split rail ring have been increased to adapt the ring to an increased groove depth. Increasing the radial depth of the split rail ring, of course, increases its radial stiffness and hence reduces its ability to conform to variations in the cylinder wall. Further, most prior two-piece oil control rings have been designed to achieve an equal spring rate or force on the top split rail and the bottom segmented rails.
An example of one such prior two-piece oil control ring may be found in U.S. Pat. No. 3,191,947, entitled PISTON RING, and issued on June 29, 1965, to Hamm. In one embodiment, the ring includes a spacer-expander having integral therewith a plurality of segments which define a bottom rail ring. The segments are alternately connected by generally vertically extending legs which are joined by a rail stop and define spring elements. The spring elements define axially extending slots which are continuous with radially extending slots defined by adjacent segments. The spring elements circumferentially alternate with a slotted leg which is bent into a box shaped in axial section. A slot defined by the leg extends axially at the inner face of the ring, radially across a horizontal portion of the leg and axially at the outer face of the ring. The spacer-expander is fabricated from a blank having alternating legs or loops of different transverse dimension. The longer loops define the box sections and the shorter loops are bent to define the spring elements.
Examples of other one-piece, two-piece and three-piece oil control rings may be found in U.S. Pat. No. 2,273,691, entitled OFFSET PISTON RING CONSTRUCTION, and issued Feb. 17, 1942, to Bowers; U.S. Pat. No. 2,635,022, entitled PISTON RING ASSEMBLY, and issued on Apr. 14, 1953, to Shirk; U.S. Pat. No. 2,859,079, entitled TRIPLE SEAL PISTON RING, and issued on Nov. 4, 1958, to Olson. U.S. Pat. No. 3,081,100, entitled PISTON RINGS, and issued on Mar. 12, 1963, to the present inventor; U.S. Pat. No. 3,124,364, entitled PISTON RING ASSEMBLY, and issued on Mar. 10, 1964, to Burns et al; U.S. Pat. No. 3,191,948, entitled PISTON RING, and issued on June 29, 1965, to Hamm; U.S. Pat. No. 3,371,938, entitled PISTON RINGS, and issued on Mar. 5, 1968, to Hamm et al; U.S. Pat. No. 3,442,519, entitled MONORAIL PISTON RING, and issued on May 6, 1969, to Hamm et al; U.S. Pat. No. 3,741,569, entitled OIL CONTROL PISTON RING, and issued on June 26, 1973, to Mayhew; and U.S. Pat. No. 4,053,164, entitled SPACER-EXPANDER FOR A PISTON OIL CONTROL RING, and issued on Oct. 11, 1977, to Saylor.